Method for making detonation cord device

ABSTRACT

A detonation device and method for making the same for use in explosive hook-up systems of the type having interconnected trunk and down lines. A core of pentaerythritol tetranitrate is compounded and constructed to substantially reduce detonation cutoffs when the lines are connected at an acute angle with respect to one another, particularly in the low grain load sizes.

United States Patent Calder, Jr. et al.

METHOD FOR MAKING DETONATION CORD DEVICE Inventors: Brooke J. Calder, Jr.; Bernard L.

Risko, both of Solon; Robert J. Belock, Twinsburg, all of Ohio Austin Powder Company, Cleveland, Ohio Filed: Feb. 5, 1973 Appl. No; 329,842

Related US. Application Data Division of Ser. No. 108,712, Jan. 22, 1971, Pat. No. 3,726,216.

Assignee:

US. Cl. 264/3 R, 149/93, 102/27 R Int. Cl C06b 21/02 Field of Search 149/93; 264/3 R; 102/27 R References Cited UNITED STATES PATENTS 6/1946 Burrows et a1 149/93 X 1 1 Jan. 14, 1975 Smith 149/93 X Gow ct al. 149/93 X Primary ExaminerStephen J. Lechert, Jr. Attorney, Agent, or Firm-Team, Teare & Sammon [57] ABSTRACT 7 Claims, 7 Drawing Figures PATENTED Q 3,860,677

- SHEEF 10F 2 M 1' 2 lo I 9 2O 2 36 v 24 28 32 Fl G.l

F162 FIGB ALTITUDE -4 A i o 0 w l J, 34 I PATENTEU JAN] 4975 SHEET 20F 2 FIG? BLEND DRY METHOD FOR MAKING DETONATION CORD DEVICE CROSS REFERENCE TO RELATED APPLICATION This application is a division of application Ser. No. 108,712 filed Jan. 22, 1971 now US. Pat. No. 3,726,216 in the names of Brooke J. Calder, Jr., Bernard L. Risko, and Robert J. Belock.

BACKGROUND OF THE INVENTION The present invention generally relates to detonating devices, and more particularly relates to an improved construction for a detonating device, such as a cord, fuse or the like, and a method of making the same for use in explosive hook-up systems of the types having interconnected trunk and down lines for detonating multiple explosive charges. The device of the invention is particularly useful in construction, excavation and mining applications where it is desirable to sequentially or simultaneously detonate a multiplicity of explosive charges via single or plural hook-up systems.

It has been known in the art to employ detonating cord or fuse as a convenient means oftransmitting the stimulus required to effect the detonation of an explosive. Such cord or fuse devices have heretofore been produced by either dry or wet loading processes, and generally include a raw core of dry or wet explosive about which is disposed an outside protective cover.

In the past, such prior devices have been employed for firing of multiple hook-up systems which include blasting machines which activate or spark electric blasting caps. Activation of the caps initiates the trunkline which produces an explosive shock or detonating wave which travels along the trunkline and down the respective down lines via various types of knot connections so as to detonate the explosive charge. Heretofore, however, difficulties have been encountered in good transmission of the shock waves from the trunkline to each of the respective down lines. In prior arrangements, it was deemed necessary to keep the respective down lines at a right angle or as close to a right angle as possible in order to prevent failures from angle cut-off in the down line during initiation thereof. Accordingly, such prior arrangements were not reliable and oftentimes resulted in dormant fuses or failures which were not only costly and time consuming to correct, but which resulted in the possibility of injury to person, or damage to property, should an explosion occur.

Explosive detonating cord may be categorized into two classes. There is the standard load size of about 50 grains per foot and higherand the so-called economy size of about grains per foot to about 40 grains per foot. While the aforesaid narrow angle juncture cutoffs are a slight problem in standard sizes, they are a major problem in the economy sizes. In the economy sizes, the explosive load is sufficiently decreased that the problem becomes of major importance and the careful tying of knots to prevent the angle cut-offs is particularly critical.

In the use of dry loaded detonating cords, a particular problem has existed. It was thought that fine granulation was to be avoided. The finer the particle size, the more difficult it was to dry load the material.

From the foregoing, the accompanying drawings, and the following description, it will be seen that the present invention provides an improved construction for a detonating device, such as a cord, fuse or the like, and a method for making the same for use, as an example, in explosive hook-up systems which provides improved results in propagating through detonation cords disposed at narrow angles to each other for detonating multiple explosive charges. The device of the invention has initiating characteristics sufficient to reliably detonate explosives, such as capsensitive explosives, without the requirement to take extreme precaution to insure that the trunklines and downlines are maintained at with respect to one another or as close thereto as possible. Moreover, the invention assures that the detonation wave will bridge or propagate through the knot connections without severing the down lines even when the latter are severely bent or slanted back in a direction toward the point of initiation. The detonating cords can be dry loaded and are particularly useful in the economy load sizes. The device of the invention is relatively rugged yet has good reliability characteristies. In addition, it provides an arrangement which allows reliable knot connections which can easily be made with minimum time and effort under practically all environmental conditions. The present invention results in a reduction in waste detonating cord or fuse material and the requirement to destroy waste pieces resulting from angular cut-offs. importantly, the increased reliability of the present invention reduces the possibility of injury to person, or damage to property. For typical prior art arrangements reference may be made to US. Pats. No. 3,155,038 and 3,320,847.

SUMMARY OF THE INVENTION The detonating device and method for making the same having improved angle cut-off characteristics for use in explosive hook-up systems of the type having interconnected trunk and down lines comprising a core of indeterminate length containing pentaerythritol tetranitrate or the like encapsulated by an outer sheath, said core material including a mixture of particles having a very fine granulation to reduce detonation cutoffs when the lines are connected at an acute angle with respect to one another in a direction toward the point of initiation. The device may be dry loaded. A correlation of parameters produce the desired result.

BRIEF DESCRIPTION OF THE DRAWINGS for determining the angular cut-offs in accordance with the present invention;

FIG. 5 is a fragmentary side elevation view of a piece of detonating cord or fuse made in accordance with the invention;

FIG. 6 is an enlarged sectional view taken along the line 6-6 of FIG. 5; and

FIG. 7 is a schematic representation showing a flow system for making the detonating device in accordance with the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring again to the drawings and in particular to FIG. 1 thereof, there is schematically illustrated a typical explosive hook-up explosive system, designated generally at S, which may be employed with the present invention. As shown, the system S includes a trunkline 2 that extends along the center of an excavation 4, such as a ditch or the like, which may be employed, for example, in a pipeline construction. In the form shown, a plurality of down lines 6, 8, 9, l and 12 are attached via connections 14, 16, 18, 20 and 22 at one end to the trunklineZ. The other ends of therespective down lines are attached to explosive charges, 24, 26, 28, 30 and 32 which may be disposed in shot holes in the ditch 4. In this hook-up, the trunkline 2 is initiated at one end by electric blasting caps 34 which, in turn, are connected in circuit to a blasting machine 36 of a type known in the art. In the invention, it is to be understood that any suitable type of hook-up system may be employed depending upon the particular] type of blasting operation.

In operation, instantaneous firing of the multiple hookup system S (FIG. I) may be achieved by actuating the blasting machine 36 which activates or sparks the electric blasting caps 34. Activation of the blasting caps 34 initiates the trunkline 2 which produces an explosive shock or detonating wave which travels along the trunkline 2 and down the respective down lines 6, 8, etc. via the bridging connections 14, 16, etc. so as to provide a substantially simultaneous detonation of the charges 24, 26, etc.

In the invention, various attachments may be made for connecting the respective down lines to the trunkline. For example, the down lines may be attached by various knot connections, such as a double wrap half hitch, loop lock clove hitch, clove hitch and the like. In FIG. 2, there is illustrated a double wrap half hitch 40 which is prepared with the down line 6, and which is drawn tightly around the trunkline 2. As shown, the trunkline 2 is oriented in the direction of initiation (as shown by arrow) which extends in a direction away from the blasting cap 34. In prior art arrangement, it was necessary to keep the respective down lines ata right angle (a) or as close to a right angle as possible in order to prevent failures from angle cut-off in the down line during initiation thereof. For example, in FIG. 3 there is illustrated a typical angle cut-off when the downline 6 slants back at an acute angle (b) in a direction toward the blasting cap or point of initiation. In such instance, the blasting effects from the trunkline 2 act to sever the down line 6, as at 42, before it is detonated through the knot 40. It is believed that such failures are caused by the explosive force, which is propagated by detonation of the trunkline, which severs the down linebefore the detonation wave has been transmitted through it via the knot connection.

Now in accordance with the invention there is provided animpr oved construction and method for mak- .ing a detonating cord or fuse device which enables detonation of multiple explosive charges substantially without cut-offs and consequent failures. Specifically, the device of the present invention enables the down line, for example, to be attached via knot connections so that, as tied, the down line may slant back at an acute angle with respect to the trunkline. In the'invention, it has been found that, as tied, the down line may be slanted at least 80 from the vertical or at an acute angle of 10 with respect to the trunkline.

In the invention, the angular disposition of the knot connection may be determined, for example, by reference to the diagrammatic representation of FIG. 4. As shown, the test may be carried out by securing a piece of detonating cord or fuse between two points A and B at a distance of 10 feet apart. Another length of cord or fuse may be secured between the points C and D to provide the proper acute angle 6. This angle may be achieved by measuring 3 feet along the hypotenuse and by adjusting the altitude to the corresponding length. A knot may then be tied with the length CD such that OD lies next to OB at the knot. The distances from theknot 'j' to each end (OC and OD) may then be recorded, the blasting cap 34 fired and any undetonated pieces measured with the distance from the knot to the cut-off recorded.

Referring now to FIGS. 5 and 6 of the drawings, there is illustrated a piece of cord or fuse which may comprise the trunkline 2 or the down line 6, for example, for use with the typical hook-up system S illustrated in FIG. 1. As shown, the fuse includes an explosive core which is encapsulated by an outer sheath, designated generally at 52, which provides a protective cover for the core. In the form shown, the sheath 52 includes an inner layer 54 which may be in the form of a fibrous tape, such as paper, which may be applied longitudinally with respect to the axis of the core 50 to provide a generally cylindrical sleeve for supporting the core in columnar relation. Though the layer 54 is preferably comprised of a fibrous material, such as crepe paper, it is to be understood that other materials, such as plastic, fiberglass-plastic composite or the like, in tape or ribbon form may be employed to give the column of explosive body during the loading operation. In the form shown, the tape for providing the layer 54 may have a width of approximately one-half inch with a thickness of about 0.003' inches. Disposed around the fibrous layer 54 is a textile layer 56 which may include 10 strands wrapped in countering relation around the layer 54. The textile layer 56 may include materials, such as cotton, rayon, jute and the like having a denier in the range from about 1,100 to about 2,200. Disposed around the textile layer 56 is another textile layer 58 which may include five strands disposed in counter relation around the layer 56. The textile layers 56 and 58 are preferably encapsulated by a relatively thin barrier layer 60. The barrier 60 is preferably made from a material having good strength and moisture impervious characteristics. Preferably, the barrier is made from a relatively thin polymeric material, such as polyethylene, polyvinyl chloride, polyethylene terephthalate or the like. The barrier 60 may be applied in ribbon or tape form and spirally wrapped in overlapping relation to provide the desired characteristics. In such case, the barrier 60 may have a thickness in the range from about 0.003 to about 0.03 inches. Disposed around the barrier layer 60 is an outer textile layer 62 which, in the form shown, may include 10 string-like strands of twisted construction which are wrapped in countered relation around the barrier 60. The textile layer 62, in turn, is covered with another textile layer 64 of similar construction, but countered in the opposite direction around the layer 62. The layers 62 and 64 may be made of the same materials and with the same denier as the inner layers 54 and 56. The layers 62 and 64 not only add protection to the core but facilitate tying of the knot connections and protect the barrier layer 62 against abrasion. The composite sheath 52 may then be provided with an outer protective layer 66. This layer is preferably comprised of a water-repellent material, such as wax or the like. This material may be dip coated or otherwise applied to the layer 64 to enhance the water-repellent characteristics of the device to facilitate making the knot connections during normal use thereof.

Turning now to a detailed reference with respect to the core 50, it has been found that consideration of the composition, physical characteristics and processing of the explosive provide the aforementioned preferred results in accordance with the invention. In the preferred embodiment, it has been found that an explosive material, such as pentaerythritol tetranitrate, (commonly referred to as PETN and sold by E. I. du Pont de Nemours & Company) provides beneficial results for the core load. In accordance with one aspect of the invention, the completed detonation cord core composition has a selected grain size mixture of very fine granulation. This final, or completed, granulation should have a maximum limit for retention of particles on a 100 mesh sieve (United States Standard Sieves being usedthroughout this disclosure) of approximately percent by weight. Preferably, less than this amount is retained on a 100 mesh sieve. Since the additives to the PETN in the core of the invention are present in small amounts, the above specified granulation parameters are applicable interchangeably to the PETN alone or to the total core composition. Such granulation is of particular need in the about 15 grains per foot to the about 40 grains per foot grain load sizes. By the novel method of loading, such grain sizes can be used in a dry loading process. This is accomplished by the use of a flow agent during loading.

It is believed that there is a correlation between the original particle size and the ultimate particle size. Too large an initial size thereafter crushed to a smaller size is believed to cause failures. It is believed that to attain the desired results, it is desirable to begin with a medium size of particles which by the loading operation are reduced to the desired particle size. It is further believed that there is a correlation between packed particle size and packed density to achieve the desired results. If the density becomes too large, it is believed that failure occurs.

A further important factor is the control of the speed of flow of the explosive material during loading.

In making the preferred embodiment, it has been found that preferred results are obtained when the PETN is selectively conditioned as to granulation, or grain size, to initially provide a mixture of medium particle size.' More particularly, it has been found that particle sizes less than those normally employed in conventional PETN detonating cords provide preferred results. Accordingly, this preferred mixture should conform to the following screen analysis:

Approximately 1 percent by weight maximum retention on a 30 mesh sieve,

From approximately 5 to approximately 15 percent by weight retention on a 100 mesh sieve,

From approximately 30 to approximately 50 percent by weight passing through a 200 mesh sieve and being retained on a 325 mesh sieve, and

Approximately 20 percent by weight maximum passing through a 325 mesh sieve. Material of this screen analysis is found to exhibit an apparent, or bulk, density from approximately 0.7 grams per cubic centimeter to approximately 0.95 grams per cubic centimeter.

The first step in the method of the preferred embodiment is to initially treat the PETN with an anti-static agent to enhance the flow characteristics of it, as desired. For example, the material may be rinsed or washed with an aqueous solution, such as an aqueous solution of the saturated, long chain or fatty alcohol sulfates sold by E. I. du Pont de Nemours & Company under the trade name Duponol G. The washed explosive is preferably filtered to remove excess of the anti-static solution and then dried to a moisture content less than approximately 1 percent by weight prior to further processing of the PETN. When employing such anti-static agent and, as dried, it is believed that the anti-static material is present in the range from approximately 5 parts per million to 1,000 parts per million, based on the weight of the PETN.

Referring now to FIG. 7 of the drawings, the steps subsequent to the rinsing of the PETN are schematically illustrated in a flow diagram wherein the drying step is illustrated schematically, as at 70. This drying step can be accomplished by means of suitable heat applicators (not shown) so as to reduce the moisture content to the desired level aforesaid, and preferably to less than approximately 0.1 percent by weight. The dried material having the selective granulation, as above specified, is then blended, as at 72, with the preferred amount of a free-flow agent so as to provide the desired free flow properties in the material. Optionally, an anti-wicking agent may be blended with the PETN contemporaneously with the blending of the flow agent. Preferably, the flow agent is of relatively fine particle size. For example, it has been found that a material classified as fumed silica sold under the trade name CAB-O-SIL sold by Cabot Corporation produces beneficial results. This material is produced by the hydrolysis of silicon tetrachloride at l,l00C. which results in a colloidal silica of high purity. The basic chemical equation for formation of this material is as follows:

This fumed silica material has considerable surface area in the range from approximately 400 square meters per gram to approximately 50 square meters per gram. In addition, such material has a sub-microscopic particle size in the range from approximately 0.007 to approximately 0.012 microns which, when blended with the PETN, enhances its free-flow characteristics. It has been found that when this agent is added to the explosive in an amount from approximately 0.05 percent to approximately 0.5 percent by weight of the PETN superior results are achieved. Moreover, it has been found that the incorporation of this flow agent in limited amounts not only enhances the flow properties of the material, but does so in a manner so as not to significantly affect the sensitivity of the explosive material. For example, it has been found that the incorporation of this flow agent provides a flow rate through an opening having a diameter of 0.18 inches of from approximately to approximately seconds per 50 grams. Another desirable characteristic of this flow agent is its water insolubility. Another water insoluble and finally divided material that may be employed is calcium stearate. Such material may be blended in an amount from approximately 0.1 to approximately 0.5 percent based on the weight of the PETN. In addition, desirable results may be achieved by mixing the fumed silica with the calcium stearate in proportions such that a major amount of silica is mixed with a minor amount of the calcium stearate.

It has been found preferable to treat the PETN with an antiwicking agent to prevent moisture and/or water from working up into the core, thereby resulting in a dormant fuse and/or detonation failures. The material employed is preferably a water-soluble polymer derived from cellulose. For example, it has been found that a material sold under the trade name CMC available from E. I. du Pont de Nemours & Company providesbeneficial results. This material is the sodium salt of carboxymethylcellulose (cellulose glycolate) formed by the reaction of high purity soda cellulose with the sodium salt of monochloroacetic acid. The reaction may be represented as;

RONa ClCH COONa ROCH COONa NaCl where R represents the cellulose structure. Other materials which may be employed include natural gums, such as guar gum and the like to provide the desired anti-wicking properties. Such agents may be added in the range from about 0.05 to 0.5 percent based on the weight of the PETN.

After the additives have been blended with the explosive material, or PETN, the core may then be formed into columnar form by providing the core with an outer sheath 52. In the preferred embodiment, this may be accomplished by employing a center thread or string 74 in conjunction with a gravity feed device, designated generally at 76. The device 76 includes a funnel-like hopper 78 having a reduced diameter neck portion 80 into which is discharged the granulated explosive mixture which flows via the string 74 under gravity through the neck 80. In a preferred form, the neck 80, for example, may have a diameter of about 0.180 inches. As the explosive charge flows through the neck 80 it is given the core shape 50 and is encapsulated by the layer of fibrous material 54 (Le, crepe paper) which may be in the form of a ribbonor tape. The inner textile layers 56 and 58 may then be applied with a tension from about 6 to 12 pounds per strand in counter relation by means of suitable textile spinning machines (not shown), as known in the art. The textile layer 58 may then be encapsulated by the polymeric layer 60 which may be applied in ribbon or tape form or by extrusion techniques, as known in the art. The outer textile layers 62 and 64 may then be applied in counter relation in a manner Similar to application of the textile layers 56 and 58. The composite fuse or cord may then be treated with the outer layer of wax 66 or the like to provide the finished article by a substantially continuous process. Accordingly, during the gravity discharge of the mixture from the hopper 78 through the neck 80 and due to the free-flow properties of the material, the

apparent or effective core density may be desirably increased, as aforesaid, without a separate crushing operation. Similarly, such increase in core density may be achieved by the amount of tension or pressure applied to the respective textile strands or yarns during the counter application thereof.

It has been found that the flow rate of loading must be adjusted so that it is neither too slow nor too fast. The desired flow rate is between seconds per 50 grams and 140 seconds per 50 grams with a measurement factor of.i8 seconds at either limit through an opening having a diameter of 0.18 inches.

In the invention, it has been found preferable to impart a vibratory force to the die 82 through which the cord or fuse is moved during the loading and encapsulating operation. Accordingly, it has been found that if the die is vibrated by means of electric vibrators 84 that the flow-rate through the restricted neck 80 may be better controlled to provide the desired core density within the limits of a particular core load.

By the foregoing process, there is provided a dryloaded detonation core which includes a core of PETN or like explosive material of very find particle granulation. In the preferred embodiment, the core composition has a screen analysis such that less than approximately 15 per cent by weight is retained on a mesh sieve. By comparing the values of the screen analysis of the core composition prior to loading with the screen analysis of the core composition after loading and formation into the core, it is foundthat less material is retained on the 100 mesh sieve in the loaded core composition, indicating fragmentation of the PETN particles during the process of forming the detonation cord. Preferably, this reduction in grain size may be expressed in terms of the number of percentage units lost in the loading process at 100 mesh and has a value of less than approximately 20 percentage units.

As previously stated, the preferred embodiment detonation cord has a grain load from approximately 15 grains per foot to approximately 40 grains per foot of the length of the device. It is in this grain load range in which the most significant improvement in low angle reliability is found. The granulation of the invention may be useful in improving low angle performance in higher grain load sizes, such as approximately 50 grains per foot and higher.

In the preferred embodiment, it is believed that it is desirable to match the very fine granulation of the PETN with a relatively low core density, such as from approximately 1.30 grams per cubic centimeter to approximately 1.55 grams per cubic centimeter.

SPECIFIC EXAMPLES Characteristics Prior to Loading (Examples l to 4) Ex.l Ex.2 Ex.3 Ex.4

Apparent density 0.82 0.87 0.84

(g/cc.) Acetone insolubles by wt.) 0.42 0.40 Moisture content by wt.) 0.04 0.04

-Continued Characteristics Prior to Loading (Examples 1 to 4) one of said loading and encapsulating steps applies sufficient force to reduce said material in particle size so that said explosive in the finished form has a granulation with a screen analysis of less than about percent by weight retained on a 100 mesh sieve so that said cord will transmit a detonation wave from another cord disposed at less than a degree angle to the first mentioned cord, and with the angle being disposed in the direction of propogation of the detonation wave along the other cord. 2. A method according to claim 1 wherein said flow rate is between 90 seconds and 140 seconds per 50 grams with a measurement factor of plus or minus 8 seconds.

3. A method of making a detonation device in accordance with claim 1, including blending the explosive material with a flow agent prior to loading.

4. A method in accordance with claim 1, wherein the mixture prior to blending has a screen analysis wherein approximately more than 99 per cent by weight passes through a 30 mesh screen.

5. A method in accordance with claim 1, including the step of vibrating the material during said loading thereof.

6. A method according to claim 1, wherein prior to loading at least approximately 50 per cent by weight of said mixture is retained on a 200 mesh sieve.

7. A detonation device according to claim 6, wherein prior to loading the explosive not more than about percent by weight of the mixture is of a screen analysis passing through a 325 mesh sieve.

Ex.l Ex.2 Ex.3 Ex.4 Flow rate 5 (sec./5O grams) 95 108 96 Screen analysis by wt.) retained on mesh 0.2 0.2 0.1 retained on mesh 03 0.9 1.1 retained on mesh 3.6 8.2 8.8 retained on 80 mesh 14.6 13.8 8.1 10 retained on 100 mesh 2.6 8.9 5.2 retained on 200 mesh 38.2 30.9 34.1 retained on 325 mesh 34.4 22.7 27.8 passed through 325 mesh 65 14.4 14.8 Granulation index 28.1 30.6 27.9

Note: Granulation index is the average of the sum of the cumulative amount on each sieve. An index of 100 represents material that is all greater than 30 mesh while an index of 0 represents material that is less than 20 325 mesh. The index is comparable only with indexes derived from the same set of sieves.

Characteristics After Loading (Examples 1 to 4) (Examples 1 to 4) Ex. 1 Ex. 2 Ex. 3 Ex. 4

Grain load (grains/ft.) 37.8 38.1 36.6 34.8 Core density (g/cc) 1.37 1.50 1.33 1.35 Apparent density (g/cc.) 0.93 1.04 1.05 1.02 Acetone insoluble 0.45 .50 0.40 0.39

(% by wt.)

Moisture by wt.) 0.02 .05 0.04 002 Screen analysis by wt.) retained on 30 mesh 0.1 0 0.1 0.0 retained on 40 mesh 01 0 0.4 0.2 retained on 50 mesh 0.2 0.1 2.4 3.6 retained on 80 mesh 3.5 1.0 8.4 6.3 retained on 100 mesh 22 3.0 3.3 1.6 retained on 200 mesh 23.4 14.0 20.9 15.6 retained on 325 mesh 42.5 24.6 35.9 44.7 passed through 325 mesh 28.0 57.3 28.6 28.0 Granulation index 16.0 9.4 19.5 17.9 Failures at 10 0 out 0 out 0 out 0 out 0f5 ofl0 of10 ofl0 Detonation speed (ft/sec.) 18.087 19,686 19.418 19,551

We claim:

1. A method of preparing a detonating cord having 50 improved angle cut-off characteristics comprising the steps of,

taking a mixture of penetaerythritol tetranitrate having a screen analysis of less than about 35 percent by weight retained on a 100 mesh sieve, and a moisture content of less than 1 percent by weight, loading the material in columnar form at a predetermined rate, and

encapsulating the column of explosive so that at least 

2. A method according to claim 1 wherein said flow rate iS between 90 seconds and 140 seconds per 50 grams with a measurement factor of plus or minus 8 seconds.
 3. A method of making a detonation device in accordance with claim 1, including blending the explosive material with a flow agent prior to loading.
 4. A method in accordance with claim 1, wherein the mixture prior to blending has a screen analysis wherein approximately more than 99 per cent by weight passes through a 30 mesh screen.
 5. A method in accordance with claim 1, including the step of vibrating the material during said loading thereof.
 6. A method according to claim 1, wherein prior to loading at least approximately 50 per cent by weight of said mixture is retained on a 200 mesh sieve.
 7. A detonation device according to claim 6, wherein prior to loading the explosive not more than about 25 percent by weight of the mixture is of a screen analysis passing through a 325 mesh sieve. 